A number of non-equilibrium work theorems [1]} have
received a lot of attention in the last 10 years, particularly after
the work of Jarzynski in 1997 [2]}, [3]}.
These theorems relate in different ways the distribution of work
performed on a system which is driven out of equilibrium to some
equilibrium thermodynamic properties. One example is the original
Jarzinsky's equality: \(\langle e^{-\beta W} \rangle = e^{-\beta \Delta F}\) , where \(W\)  is the work performed on the system that has been
driven (out-of-equilibrium) by varying an external control parameter
\(H\)  changing from \(H(0)\)  to \(H(1)\) , and \(\Delta F\)  is the free energy
difference between two states 0 and 1 that correspond to the
equilibrium states at \(H(0)\)  and \(H(1)\) . The average \(\langle \cdot \rangle \)  should be understood as obtained after many repetitions of
the driving process. The system is assumed to be in contact with a
heat bath at temperature \(\beta ^{-1}\)  which generates an statistical
ensemble of copies of the system which is the source of work
fluctuations. Most of these theorems have been experimentally
verified. [4]}, [5]}
